The invention relates to a drive device of the type specified in the preamble of claim 1 for an automotive work machine. The invention further relates to an automotive work machine with a drive device as well as to a method for operating a drive device of an automotive work machine.
Conventional drive devices for mobile work machines are driven by hydraulic motors. However, the operating range of a hydraulic motor usually does not allow covering the entire drive range of the work machines from maximum traction force at small speeds up to the maximum traveling speed. Therefore, conventional drive devices have two shift states, the first shift state of which with greater gear ratio is adapted for slow speeds and large traction forces and the second shift state of which with lower gear ratio is adapted for fast speeds and lower traction forces. Therein, a hydraulic motor usually remains permanently engaged with constant gear ratio and covers the entire speed range with low traction force. A second hydraulic motor is connected for torque addition with greater gear ratio in order to allow large traction forces at small speeds. Due to the greater gear ratio, however, the second hydraulic motor reaches its rotation speed limit already at relatively low speed and therefore has to be decoupled at larger speeds. However, the change of the shift states is only possible in standstill in many drive devices.
Various concepts exist in order to allow passing through the entire speed range without interruption of the traction force. For example, from DE 44 04 829 A1, a drive device can be gathered, which includes a superposition transmission, two hydraulic motors and several multi-disk clutches among other things. In order to change the gear ratio during travel, with which the second hydraulic motor is connected, the coupling of the second hydraulic motor is changed over from a sun gear shaft to a ring gear of a planetary gearing. This allows that the work machine can pass through the entire speed range without interruption of the traction force, because a hydraulic motor remains permanently connected and thereby provides a torque even during the shifting operation.
However, the circumstance is to be considered disadvantageous in such a drive device that both hydraulic motors have to obtain an own hydraulic drive determined by the system. Thus, at least two pumping devices are always required for the traction drive. Moreover, multiple multi-disk clutches, multiple rotary feedthroughs and a pumping device are required in order to keep the pressure constant on the multi-disk clutches. This results in a correspondingly high installation space requirement of the drive device as well as in high manufacturing costs.
In addition, drive devices are known, in which one of two hydraulic motors is engaged and disengaged with a multi-disk clutch. However, the multi-disk clutch has to be configured such that it is able to securely transmit the full torque of the hydraulic motor. In addition, in these concepts, the multi-disk clutch is usually disposed on a center shaft in order to avoid too high rotation speeds at large speeds on the then disengaged drive branch, whereby the torque maximally to be transmitted becomes even larger. Here too, a separate pumping device is therefore required in order to be able to provide a sufficient pressure for the multi-disk clutch on all operating conditions. Alternatively, the clutch is fed by the feed pressure of the hydrostatic traction drive available anyway. However, this feed pressure can usually vary by the factor of 3, for example between about 10 bar and about 30 bar, such that the friction power on the multi-disk clutch also considerably varies. Therefore, the multi-disk clutch has to be capable of transmitting the required torque even with comparatively low feed pressure. However, this requires a comparatively large dimensioning of the multi-disk clutch, whereby the installation space requirement and the manufacturing costs of the drive device in turn significantly increase.